Creating BCRYPT_ECCKEY_BLOB from a compressed key using Windows APIs only

To create a BCRYPT_ECCKEY_BLOB from a compressed key using only Windows APIs, you can follow these steps:

1. Obtain the compressed key data: Obtain the compressed ECC key data that you want to convert to the BCRYPT_ECCKEY_BLOB format. This could be the compressed public key or any other compressed key data you have.

2. Create a BCRYPT_ECCKEY_BLOB structure: Create an instance of the BCRYPT_ECCKEY_BLOB structure and populate its members with the necessary information.

   c++Copy code
   BCRYPT_ECCKEY_BLOB ecckeyBlob;
   
   ecckeyBlob.dwMagic = BCRYPT_ECDSA_PUBLIC_P256_MAGIC;
   
   ecckeyBlob.cbKey = keyDataSize;  // Size of the compressed key data
   
   // Set other relevant members of the structure if needed
   
   

   Adjust the dwMagic value according to the specific elliptic curve and key type you are working with.

3. Allocate memory and copy the compressed key data: Allocate memory for the key data buffer and copy the compressed key data into it.

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   BYTE* keyDataBuffer = new BYTE[keyDataSize];
   
   memcpy(keyDataBuffer, compressedKeyData, keyDataSize);  // Copy the compressed key data into the buffer
   
   ecckeyBlob.X = keyDataBuffer;
   
   

   Replace compressedKeyData with the actual pointer to your compressed key data.

4. Use the BCRYPT_ECCKEY_BLOB structure: You can now use the ecckeyBlob structure in your further operations, such as importing the key using BCryptImportKeyPair or BCryptImportKey.

   Remember to clean up the allocated memory and resources when you are done working with the BCRYPT_ECCKEY_BLOB structure.

Note that the code provided above is a simplified example for creating a BCRYPT_ECCKEY_BLOB from compressed key data using Windows APIs. Depending on your specific requirements and scenario, additional steps or adjustments may be necessary. It's important to consult the official Microsoft documentation for the relevant Windows APIs and structures, as well as to handle any errors or exceptions that may occur during the process.